Method for forming bump on electrode pad with use of double-layered film

ABSTRACT

A process for forming bumps on electrode pads for a wiring board including a substrate and a plurality of electrode pads. The process (a) forms a laminated two-layer film on the wiring board and forms a pattern of apertures at positions corresponding to the electrode pads, the laminated two-layer film including a lower layer containing an alkali-soluble radiation-nonsensitive resin composition and an upper layer containing a negative radiation-sensitive resin composition; (b) fills a low-melting metal in the aperture pattern; (c) reflows the low-melting metal by pressing or heating to form bumps; and (d) peels and removes the laminated two-layer film from the board. The laminated film including two layers with different properties permits high resolution and easy peeling.

FIELD OF THE INVENTION

The present invention relates to a process for forming low-melting metalbumps such as solder bumps used in the mounting of IC chips on amultilayer printed wiring board.

BACKGROUND OF THE INVENTION

Low-melting metal bumps such as solder bumps are used for the mountingof IC chips and the like. Formation of such bumps takes place on the ICchips or on the multilayer printed wiring board.

BGA (ball grid array) is a form of package in which the bumps areprovided to an IC chip. This term generally refers to a package in whichthe IC chip is mounted on a package substrate.

WL-CSP (wafer level-chip size packaging) is a new technology for thehigh-density mounting. In the WL-CSP, a plurality of IC chip circuits isformed on one wafer and collectively subjected to electrode formation,packaging and burn-in test; thereafter the wafer is cut into IC chippackages.

Collective electrode formation in the WL-CSP may be performed byelectrolytic deposition, filling a metal paste followed by reflowing, orplacing metal balls followed by reflowing.

The increase of IC chip density has lead to higher density andminiaturization of bumps on the IC chip. Solder bumps have increasinglybeen studied and been in practical use in the WL-CSP mounting technologybecause they allow both connection reliability and reduction ofprocessing cost. Specifically, the solder bumps are formed byelectrolytic deposition using a mask that is produced by patterning afilm of at least 50 μm thickness formed by application or lamination ofa positive or negative liquid resist or dry film.

Meanwhile, when the solder bumps are provided to a multilayer printedwiring board, a solder resist layer is formed on the wiring board toprevent fusion bonding between the solder bumps. The solder resist layeris provided with apertures at positions corresponding to electrode pads.To form the solder bumps in the solder resist layer, mask printing of asolder paste is performed. The mask used in the mask printing has apattern (pattern of apertures) that corresponds to the apertures of thesolder resist layer. In carrying out the mask printing, the mask isplaced on the solder resist layer so as to align the mask pattern andthe apertures of the solder resist layer. The solder paste is thenprinted through the mask within the apertures of the solder resist layeron the electrode pads; subsequently, the solder paste is reflowed toform solder bumps on the electrode pads.

A variety of studies have been made to cope with reduction of solderbump pitches. For example, JP-A-H10-350230 discloses formation of apeelable solder dam resist on a solder resist, and JP-A-2000-208911discloses a method wherein a dry film is laminated on the solder resistlayer, apertures are created at positions corresponding to electrodepads, a solder paste is applied followed by reflowing, and the dry filmis peeled.

In the aforementioned process of bump formation, the positive resist,although easily peelable in general, causes difficult control of theaperture pattern configuration, often resulting in nonuniform bump size.

On the other hand, the negative resist permits relatively easy controlof pattern shape, but is generally difficult to peel because of itsphotocrosslinking characteristics. In particular, when the solder bumpsare formed by filling and reflowing the paste, the resist becomes evenmore difficult to peel from the board because the crosslinking in thenegative resist proceeds to a further extent by the heat applied in thereflowing.

The resist film peeling is generally performed by spray method with anaqueous solution of sodium hydroxide or sodium carbonate. For thedry-film or liquid negative resist, dip method has been increasinglyemployed with use of a peeling solution that contains a highly polarsolvent and an organic alkali. The former method, although inexpensive,often results in residual resist around the bumps having a high density,and causes deterioration of the bumps. The latter method hasdisadvantages that the peeling solution is expensive, and the metalsurface of the bumps and the underlying board surface are corroded whenthe organic alkali concentration and the peeling solution temperatureare increased for improving the peeling efficiency per amount of thepeeling solution.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the aforesaid problems. Asshown in FIGS. 1(a) and 5(a), a laminated two-layer film is formed on awiring board, which two-layer film includes a lower layer comprising analkali-soluble radiation-nonsensitive resin composition and an upperlayer comprising a negative radiation-sensitive resin composition.Thereafter, photoexposure and development are performed one time tocreate a pattern of apertures for bump formation at positionscorresponding to electrode pads.

The laminated film of the invention includes two layers having differentproperties, so that both high resolution and easy peeling property areachieved. Namely, the use of the lower layer that comprises a compoundhaving a phenolic hydroxyl group leads to the following effects:

(1) The lower layer exhibits adequate alkali developability to permitpatterning by one operation of photoexposure and development.

(2) The phenolic hydroxyl group in the resin composition of the lowerlayer functions to deactivate photo-radicals to inhibit curing reactionat the interfaces between the upper and lower layers and between thelower layer and the board even if intermixing of the upper and lowerlayers has taken place. As a result, good peelability of the laminatedtwo-layer film can be maintained.

Accordingly, the negative resist traditionally unsuitable for use due topoor peelability can be used as upper layer. The use of the negativeresist as the upper layer permits sufficient mechanical strength of theresist pattern required in the step of filling a low-melting metal intothe bump-formation aperture pattern as illustrated in FIG. 1(b) or 5(b).

Furthermore, the lower layer has excellent peelability such that it canbe peeled even by single use of a highly polar organic solvent such asdimethyl sulfoxide or N-methylpyrrolidone. The peeled pieces have theupper layer that has been crosslinked and is hardly soluble in suchhighly polar organic solvents. Accordingly, the peeled pieces can beeasily removed by precipitation separation or cycle filtration.

When the peel treatment employs a peeling apparatus having multistageimmersion baths, the treatment may be designed to peel most of thenegative resist film in the first bath containing the organic solvent,and to remove the residues of the lower layer in the second and laterbaths filled with a peeling solution containing an alkali component.Thus, the peeling efficiency can be improved without increasing thealkali concentration of the peeling solution, and the damage to thesolder bumps and the underlying board can be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating a process of bumpformation according to the present invention;

FIG. 2 is a schematic sectional view illustrating a process of bumpformation according to the present invention;

FIG. 3 is a schematic sectional view illustrating a process of bumpformation according to the present invention;

FIG. 4 is a schematic sectional view illustrating a process of bumpformation according to the present invention;

FIG. 5 is a schematic sectional view illustrating a process of bumpformation according to the present invention;

FIG. 6 is a schematic sectional view illustrating a process of bumpformation according to the present invention;

FIG. 7 is a schematic sectional view illustrating a process of bumpformation according to the present invention; and

FIG. 8 is a schematic sectional view illustrating a process of bumpformation according to the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereinbelow, the process of bump formation according to the presentinvention will be described with reference to the drawings.

A first embodiment of the process for forming bumps on electrode padsaccording to the invention will be explained in great detail withreference to FIG. 2. In the present embodiment, a wiring board includesa silicon wafer 203 as substrate, and a plurality of electrode pads 201provided on the substrate surface. Bump-formation apertures 220 arefilled with a low-melting metal paste represented by solder paste. Apassivation film 202 is formed so as to embed the side surfaces and endsurfaces of the electrode pads 201.

FIG. 2(a) shows a sectional structure of a semiconductor chip wafer inwhich the electrode pads 201 are arranged so as to form an area over theentire surface of the semiconductor. When the electrode pads 201 havebeen formed on the silicon wafer 203, the wiring board is covered withthe passivation film 202 having a thickness of, for example, 1 μm, so asto expose the major surface of the electrode pads 201.

As illustrated in FIG. 2(b), an electrode metal diffusion preventionfilm 204 is formed over the entire surface of the electrode pads 201 andthe passivation film 202, by sputtering, deposition or the like. Themetal diffusion prevention film 204 is formed using any of Ni, Cr, TiN,TaN, Ta, Nb and WN, and in a thickness of, for example, 1 μm. The metaldiffusion prevention film 204 may be a single film or a laminated film.

As illustrated in FIG. 2(c), a barrier metal layer 205 is formed overthe entire surface of the wiring board in which the metal diffusionprevention film 204 has been fabricated. The barrier metal layer may beproduced by depositing a film of a barrier metal selected from Ti, Ni,Pd and Cu in a thickness of several thousands of angstroms with use of asputtering apparatus or an electron-beam deposition apparatus.

As shown in FIG. 2(d), a laminated two-layer film is formed on thewiring board having the barrier metal layer 205. The laminated two-layerfilm includes a lower layer 206 comprising an alkali-solubleradiation-nonsensitive resin composition and an upper layer 207comprising a negative radiation-sensitive resin composition.

For example, the lower layer 206 may be formed by applying a liquidlower layer material in a thickness of 2 to 3 μm. Thereafter, the upperlayer 207 may be formed on the lower layer 206 by applying a liquidnegative resist or laminating a negative dry film resist in a thicknessof at least 50 μm. The resultant laminated two-layer film consisting ofthe lower and the upper layers 206 and 207 is irradiated with radiationthrough a mask and then developed to produce bump-formation apertures220 at positions that correspond to bump formation positions above theelectrode pads 201.

Possible combinations of the resists, including that in the aboveprocess, for forming the laminated two-layer film are for example:

(1) A liquid resist for the lower layer, and a liquid resist for theupper layer

(2) A liquid resist for the lower layer, and a dry film resist for theupper layer

(3) A dry film resist for the lower layer, and a liquid resist for theupper layer

(4) A dry film resist for the lower layer, and a dry film resist for theupper layer

(5) A two-layer dry film resist having a lower layer/upper layerstructure

As illustrated in FIG. 2(e), a low-melting metal paste 208, such as asolder paste, is filled in the bump-formation apertures 220 with use ofa squeegee 209 or the like.

Referring to FIGS. 2(f) and (g), the wiring board with the metal pastefilled therein is heated in a nitrogen atmosphere, and the metal pasteis reflowed to produce bumps 210.

Subsequently, the laminated film is peeled as shown in FIG. 2(h). Thewiring board is then electrically tested and diced into chips. The chipsare subjected to the flip chip bonding.

Although the above-described embodiment employs a solder paste as thelow-melting metal paste, good reliability may be obtained by use of amixture of metals such as Sn, Pb, Ag, Bi, Zn, In, Sb, Cu, Bi and Ge. Inthe above embodiment, the low-melting metal bumps, preferably solderbumps, are produced by filling the metal into the bump-formationapertures 220 with use of the squeegee. It is also possible that thebumps are formed by placement of low-melting metal balls (solder balls)308 as shown in FIG. 3 (second embodiment) or by electrolytic depositionof a low-melting metal film 408 as shown in FIG. 4 (third embodiment).

After the metal paste is reflowed, flux cleaning may be performed.

FIGS. 5(a) to (d) explain formation of bumps on a multilayer printedwiring board by the process of the invention. Although FIG. 5illustrates one conductive circuit and one insulating resin interlayer,pluralities of these circuits and layers are generally present inalternate order.

A fourth embodiment of the process for forming bumps on electrode padsaccording to the invention will be explained with reference to FIG. 6.In the present embodiment, a wiring board comprises a substrate 615comprising glass epoxy resin or BT (bismaleimide-triadine) resin, aninsulating resin interlayer 602 overlaid on the substrate, a pluralityof electrode pads 605, and a solder resist 611 formed so as to embed theside surfaces of the electrode pads. Bump-formation apertures 608 arefilled with a low-melting metal paste 610, typically a solder paste,with use of a squeegee.

FIG. 6(a) shows a sectional structure of a wiring board in which theelectrode pads 605 are arranged so as to form an area over the entiresurface of the semiconductor. The wiring board used in this embodimentis a multilayer laminated board that includes the insulating resininterlayer 602 and the conductive circuits 603 on the glass epoxy resin615. The conductance across the thickness of the board is obtainedthrough via holes 604 formed by deposition. The solder resist 611 isapplied over the insulating resin interlayer 602 and developed to createapertures at positions corresponding to the electrode pads therebelow.The conductive circuits 603 are partially exposed at the bottom of theapertures, and the electrode pads 605 are formed on the exposedconductive circuits 603 by electroless deposition.

As shown in FIG. 6(b), a laminated two-layer film is formed on thesolder resist 611. The laminated two-layer film includes a lower layer606 comprising an alkali-soluble radiation-nonsensitive resincomposition and an upper layer 607 comprising a negativeradiation-sensitive resin composition.

For example, the lower layer 606 maybe formed by applying a liquid lowerlayer material in a thickness of 2 to 3 μm. Thereafter, the upper layer607 maybe formed on the lower layer 606 by applying a liquid negativeresist or laminating a negative dry film resist in a thickness of atleast 40 μm. The resultant laminated film is photoexposed to create alatent pattern and then developed to produce solder-bump-formationapertures 608 at positions that correspond to bump-formation positionsabove the electrode pads 605.

Similarly to the aforementioned embodiment using the silicon wafersubstrate, possible combinations of the resists, including that in theabove process, for forming the laminated two-layer film are for example:

(1) A liquid resist for the lower layer, and a liquid resist for theupper layer

(2) A liquid resist for the lower layer, and a dry film resist for theupper layer

(3) A dry film resist for the lower layer, and a liquid resist for theupper layer

(4) A dry film resist for the lower layer, and a dry film resist for theupper layer

(5) A two-layer dry film resist having a lower layer/upper layerstructure

As illustrated in FIG. 6(c), a low-melting metal paste 610, such as asolder paste, is filled in the bump-formation apertures 608 with use ofa squeegee 609 or the like.

Referring to FIGS. 6(d) and (e), the wiring board with the metal pastefilled therein is heated in a nitrogen atmosphere, and the metal pasteis reflowed to produce bumps.

Subsequently, the laminated film is peeled as shown in FIG. 6(f).

Although the above-described embodiment employs a solder paste as thelow-melting metal paste, good reliability may be obtained by use of amixture of metals such as Sn, Pb, Ag, Bi, Zn, In, Sb, Cu, Bi and Ge. Inthe above embodiment, the low-melting metal bumps, preferably solderbumps, are formed by filling the metal into the bump-formation apertures608 with use of the squeegee. It is also possible that the bumps areformed by placement of low-melting metal balls (solder balls) 708 asshown in FIG. 7 (fifth embodiment) or by electrolytic deposition of alow-melting metal film 808 as shown in FIG. 8 (sixth embodiment).

After the metal paste is reflowed, flux cleaning may be performed.

Hereinbelow, materials of the lower and upper layers for use in thepresent invention will be described.

Lower Layer

The lower layer is not particularly limited as long as it contains analkali-soluble compound, preferably an alkali-soluble compound having aphenolic hydroxyl group. Desirably, the lower layer has a compositiondescribed below.

For the formation of the lower layer, a lower layer material is usedthat contains an alkali-soluble radiation-nonsensitive resincomposition. The lower layer material may be a liquid or a dry film.

[Alkali-Soluble Compound Having a Phenolic Hydroxyl Group: Component A]

The above title compounds (hereinafter, the compounds (A)) are broadlydivided into low-molecular weight compounds having up to 10 phenolskeletons, and high-molecular weight polymers such as novolak resins andpoly(4-hydroxystyrene).

When the low-molecular weight compound (A) is employed, a developingsolution used for forming the apertures is preferably one relativelyweak in alkalinity such as sodium carbonate. In the case of thehigh-molecular weight polymer, a developing solution used for formingthe apertures is preferably one relatively strong in alkalinity such astetramethylammoniumhydroxide.

Examples of the low-molecular weight compounds include4,4′-[1-[4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]diphenol,methyl 2,2-bis(1,5-dimethyl-4-hydroxyphenyl)propionate and4,6-bis[1-(4-hydroxyphenyl)-1-methylethyl]-1,3-benzenediol.

Compounds generally used as thermal polymerization inhibitors may alsobe used. Examples thereof include pyrogallol, benzoquinone,hydroquinone, methylene blue, tert-butylcatechol, monobenzyl ether,methylhydroquinone, amylquinone, amyloxyhydroquinone, n-butylphenol,phenol, hydroquinone monopropyl ether,4,4′-(1-methylethylidene)bis(2-methylphenol),4,4′-(1-methylethylidene)bis(2,6-dimethylphenol), 4,4′,4″-ethylidenetris(2-methylphenol), 4,4′,4″-ethylidene trisphenol and1,1,3-tris(2,5-dimethyl-4-hydroxyphenyl)-3-phenylpropane.

Examples of the high-molecular weight polymers include polymers having aphenolic hydroxyl group, such as novolak resins and polyhydroxystyrenedescribed below, and derivatives thereof. They may be used singly or incombination.

(Novolak Resins)

The alkali-soluble novolak resins for use in the invention arecondensation products of m-cresol, one or more types of other phenols,and an aldehyde compound. The alkali-soluble novolak resins are notparticularly limited, provided that the m-cresol has a proportion of 50to 90 mol % relative to all the phenols.

Examples of the other types of phenols as materials of the novolakresins include 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 3,4-xylenol,3,5-xylenol and 2,3,5-trimethylphenol. These maybe used eitherindividually or in combination or two or more kinds.

Of the above phenols, 2,3-xylenol, 2,4-xylenol, 3,4-xylenol and2,3,5-trimethylphenol are preferable.

Preferred examples of m-cresol/phenol(s) combinations includem-cresol/2,3-xylenol, m-cresol/2,4-xylenol,m-cresol/2,3-xylenol/3,4-xylenol, m-cresol/2,3,5-trimethylphenol andm-cresol/2,3-xylenol/2,3,5-trimethylphenol.

Suitable aldehyde compounds for use in the condensation includeformaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde,o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde,glyoxal, glutaraldehyde, terephthalaldehyde and isophthalaldehyde. Ofthese, formaldehyde and o-hydroxybenzaldehyde are particularly suitable.

These aldehyde compounds maybe used either individually or incombination or two or more kinds. Preferably, the aldehyde compound(s)will be used in an amount of 0.4 to 2 mol, and more preferably 0.6 to1.5 mol per mol of the phenols.

The condensation between the phenols and the aldehyde compound isusually carried out in the presence of an acid catalyst. Exemplary acidcatalysts include hydrochloric acid, nitric acid, sulfuric acid, formicacid, oxalic acid, acetic acid, methanesulfonic acid andp-toluenesulfonic acid. Generally, the acid catalyst may be used in anamount of 1×10⁻⁵ to 5×10⁻¹ mol per mol of the phenols.

The condensation is usually performed using water as reaction medium.When it is expected that the reaction system will be heterogeneous froman early stage of the reaction, the water as the reaction medium may bereplaced by:

an alcohol such as methanol, ethanol, propanol, butanol or propyleneglycol monomethyl ether;

a cyclic ether such as tetrahydrofuran or dioxane; or

a ketone such as ethyl methyl ketone, methyl isobutyl ketone or2-heptanone.

The reaction medium may be used in an amount of 20 to 1,000 parts byweight per 100 parts by weight of the reactants.

Although the condensation temperature may be appropriately adjusteddepending on the reactivity of the reactants, it is generally in therange of 10 to 200° C.

The condensation reaction may be carried out in an appropriate manner.For example, the phenols, the aldehyde compound, the acid catalyst, etc.may be introduced into a reactor all at once. Alternatively, thephenols, the aldehyde compound, etc. may be added with progress of thereaction in the presence of the acid catalyst.

After completion of the condensation, the unreacted materials, the acidcatalyst, the reaction medium, etc. are removed from the system. Forexample, this can be made through a process in which the temperature inthe reaction system is increased to 130 to 230° C. and the volatilecomponents are evaporated under reduced pressure to recover the novolakresin. Alternative is a process in which the novolak resin obtained isdissolved in a good solvent, followed by mixing with a poor solvent suchas water, n-hexane or n-heptane, and the precipitated phase of resinsolution is separated to recover the high-molecular weight novolakresin. The good solvents include ethylene glycol monomethyl etheracetate, methyl 3-methoxypropionate, ethyl lactate, methyl isobutylketone, 2-heptanone, dioxane, methanol and ethyl acetate.

The novolak resins preferably have a weight-average molecular weight interms of polystyrene (hereinafter the “Mw”) of 2,000 to 20,000, andparticularly preferably 3,000 to 15,000, from the viewpoints ofworkability of the composition into films, and developability,sensitivity and heat resistance of the resulting resist.

(Polyhydroxystyrenes)

Suitable polyhydroxystyrenes for use in the invention include resinscommercially available under the trade names of MARUKA LYNCUR M, MARUKALYNCUR CMM, MARUKA LYNCUR CHM, MARUKA LYNCUR MB, MARUKA LYNCUR PHM-C,MARUKA LYNCUR CST and MARUKA LYNCUR CBA (Maruzen Petrochemical Co.,Ltd.).

[Solvent: Component B]

A solvent may be employed for dissolving the component A to prepare acoating solution. The solvents are not particularly limited as long asthe component A is favorably dissolved therein. Examples thereof includeethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol monomethyl ether acetate, ethylene glycol monoethylether acetate, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, propylene glycol monomethyl ether acetate, propyleneglycol monopropyl ether acetate, toluene, xylene, methyl ethyl ketone,2-heptanone, 3-heptanone, 4-heptanone, cyclohexanone, ethyl2-hydroxypropionate, ethyl 2-hydroxy-2-methylpropionate, ethylethoxyacetate, ethyl hydroxyacetate, methyl 2-hydroxy-3-methylbutanoate,methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, ethyl3-methoxypropionate, butyl acetate, methyl pyruvate and ethyl pyruvate.Also usable are high-boiling solvents such as N-methylformamide,N,N-dimethylformamide, N-methylformanilide, N-methylacetamide,N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, benzylethyl ether, dihexyl ether, acetonylacetone, isophorone, caproic acid,caprylic acid, 1-octanol, 1-nonanol, benzyl alcohol, benzyl acetate,ethyl benzoate, diethyl oxalate, diethyl maleate, γ-butyrolactone,ethylene carbonate, propylene carbonate and ethylene glycol monophenylether acetate. These solvents may be used singly or in combination oftwo or more kinds. Of these, ethyl 2-hydroxypropionate and propyleneglycol monomethyl ether acetate are preferable.

[Acrylic Resin: Component C]

An alkali-soluble acrylic resin may be added in order to improveapplication properties and to stabilize coating film properties,particularly when the component A is the low-molecular weight compoundhaving a phenolic hydroxyl group.

The composition of the acrylic resin is not particularly limited,provided that the resin contains a unit derived from a (meth) acrylicester, and a unit imparting alkali solubility that is derived from aradically polymerizable compound having a carboxyl group and/or aphenolic hydroxyl group.

Examples of the radically polymerizable compounds having a carboxylgroup include acrylic acid and methacrylic acid.

Examples of the radically polymerizable compounds having a phenolichydroxyl group include vinyl monomers having a phenolic hydroxyl group,such as p-hydroxystyrene, m-hydroxystyrene, o-hydroxystyrene,α-methyl-p-hydroxystyrene, α-methyl-m-hydroxystyrene,α-methyl-o-hydroxystyrene, 4-isopropenylphenol, 2-allylphenol,4-allylphenol, 2-allyl-6-methylphenol, 2-allyl-6-methoxyphenol,4-allyl-2-methoxyphenol, 4-allyl-2,6-dimethoxyphenol and4-allyloxy-2-hydroxybenzophenone. These compounds may be used eitherindividually or in combination of two or more kinds. Of the compounds,p-hydroxystyrene and 4-isopropenylphenol are preferred.

The acrylic copolymer contains 1 to 60 wt %, preferably 5 to 50 wt % theunit derived from the carboxyl-containing radically polymerizablecompound and/or the unit derived from the phenolic hydroxyl-containingradically polymerizable compound. When the amount is less than 5 wt %,the acrylic copolymer becomes less soluble in the alkaline developingsolution, so that the developing results in residual film and poorresolution. When the amount exceeds 50 wt %, the acrylic copolymer hastoo high a solubility in the alkaline developing solution, so that thetwo-layer film will have apertures with undercuts.

[Surfactant: Component D]

A surfactant may be added to the composition in order to improveapplication, defoaming and leveling properties. Suitable surfactantsinclude fluorine-containing surfactants commercially available under thetrade names of BM-1000 and BM-1100 (manufactured by BM Chemie); MEGAFACEseries F142D, F172, F173 and F183 (manufactured by Dainippon Ink andChemicals, Incorporated); FLUORAD series FC-135, FC-170C, FC-430 andFC-431 (manufactured by Sumitomo 3M); SURFLON series S-112, S-113,S-131, S-141 and S-145 (manufactured by Asahi Glass Co., Ltd.); andSH-28PA, SH-190, SH-193, SZ-6032 and SF-8428 (manufactured by Toray DowCorning Silicone Co., Ltd.). The amount of the surfactant is preferablynot more than 5 parts by weight per 100 parts by weight of the copolymer(A).

The lower layer material may contain other components. Specific examplesthereof include phenol novolak epoxy resins, cresol novolak epoxyresins, bisphenol epoxy resins, trisphenol epoxy resins, tetraphenolepoxy resins, phenol-xylylene epoxy resins, naphthol-xylylene epoxyresins, phenol-naphthol epoxy resins, phenol-dicyclopentadiene epoxyresins and alicyclic epoxy resins. Inorganic fillers are alsoemployable. Specific examples of the inorganic fillers include silica,aluminum hydroxide and barium sulfate. Other employable additives arepolymer additives, reactive diluents, leveling agents, wettabilityimprovers, plasticizers, antioxidants, antistatic agents,mildew-proofing agents, moisture conditioners and flame-retardants.

Upper Layer

For the formation of the upper layer, an upper layer material is usedthat contains a negative radiation-sensitive resin composition. Theupper layer material may be a liquid or a dry film.

The radiation-sensitive resin compositions as described inJP-A-H08-301911 may be employed as the negative radiation-sensitiveresin composition.

The negative radiation-sensitive resin composition used in the inventionincludes an acrylic resin (the above component C), a crosslinking agent(component E), an initiator (component F), a solvent (the abovecomponent B), and a surfactant (the above component D).

[Crosslinking Agent: Component E]

Exemplary crosslinking agents (components E) include trimethylolpropanetri(meth)acrylate, pentaerythritol tri(meth)acrylate, ethylene glycoldi(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethyleneglycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, butyleneglycol di(meth)acrylate, propylene glycol di(meth)acrylate,trimethylolpropane di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate,tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate,tris(2-hydroxyethyl)isocyanurate di(meth)acrylate,tricyclodecanedimethanol di(meth)acrylate, epoxy (meth)acrylate obtainedby adding a (meth)acrylic acid to diglycidyl ether of bisphenol A,bisphenol A-di(meth)acryloyloxyethyl ether, bisphenolA-di(meth)acryloyloxy ethyloxy ethyl ether, bisphenolA-di(meth)acryloyloxyloxy methyl ethyl ether, tetramethylolpropanetetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol penta(meth)acrylate anddipentaerythritol hexa(meth)acrylate.

Commercially available compounds may be used as the crosslinking agents(components E). Examples thereof include compounds commerciallyavailable under the trade names of ARONIX series M-210, M-309, M-310,M-400, M-7100, M-8030, M-8060, M-8100, M-9050, M-240, M-245, M-6100,M-6200, M-6250, M-6300, M-6400 and M-6500 (manufactured by Toagosei Co.,Ltd.); KAYARAD series R-551, R-712, TMPTA, HDDA, TPGDA, PEG400DA, MANDA,HX-220, HX-620, R-604, DPCA-20, DPCA-30, DPCA-60 and DPCA-120(manufactured by Nippon Kayaku Co., Ltd.); and Biscoat series Nos. 295,300, 260, 312, 335HP, 360, GPT, 3PA and 400 (manufactured by OsakaOrganic Chemical Industry Ltd.)

These crosslinking agents (components E) may be used singly or incombination of two or more kinds. Preferably, the crosslinking agent isused in an amount of 10 to 250 parts by weight, more preferably 20 to200 parts by weight, and particularly preferably 25 to 150 parts byweight per 100 parts by weight of the acrylic resin (component C). Whenthe amount is less than 10 parts by weight, the photosensitivity tendsto be lowered. When the amount exceeds 250 parts by weight, thecompatibility with the copolymer (A) will be deteriorated, leading topoor storage stability and difficulties in achieving the film thicknessof 20 μm or more.

[Radiation-Induced Radical Polymerization Initiator: Component F]

Examples of the radiation-induced radical polymerization initiators(hereinafter, the initiators or components (F)) for use in the inventioninclude α-diketones such as benzyl and diacetyl; acyloins such asbenzoin; acyloin ethers such as benzoin methyl ether, benzoin ethylether and benzoin isopropyl ether; benzophenones such as thioxanthone,2,4-diethyl thioxanthone, thioxanthone-4-sulfonic acid, benzophenone,4,4′-bis(dimethylamino)benzophenone and4,4′-bis(diethylamino)benzophenone; acetophenones such as acetophenone,p-dimethylaminoacetophenone, α,α-dimethoxy-α-acetoxybenzophenone,α,α-dimethoxy-α-phenylacetophenone, p-methoxyacetophenone,1-[2-methyl-4-methylthiophenyl]-2-morpholino-1-propanone,α,α-dimethoxy-α-morpholino-methylthiophenyl acetophenone and2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butane-1-one; quinonessuch as anthraquinone and 1,4-naphthoquinone; halides such as phenacylchloride, tribromomethylphenylsulfone and tris(trichloromethyl)-s-triazine; bisimidazoles such as[1,2′-bisimidazole]-3,3′,4,4′-tetraphenyl and[1,2′-bisimidazole]-1,2′-dichlorophenyl-3,3′,4,4′-tetraphenyl; peroxidessuch as di-tert-butyl peroxide; and acylphosphine oxides such as2,4,6-trimethylbenzoyldiphenylphosphine oxide. Commercially availableinitiators include IRGACURE series 184, 651, 500, 907, CGI369 andCG24-61 (manufactured by Ciba Specialty Chemicals Inc.); LUCIRIN LR8728and LUCIRIN TPO (manufactured by BASF); DAROCUR series 1116 and 1173(manufactured by Ciba Specialty Chemicals Inc.); and UBECRYL P36(manufactured by UCB). Where necessary, the above radiation-inducedradical polymerization initiators may be used in combination withhydrogen donor compounds such as mercaptobenzothiazole andmercaptobenzoxazole.

Of the radiation-induced radical polymerization initiators, preferableare the acetophenones such as1-[2-methyl-4-methylthiophenyl]-2-morpholino-1-propanone,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butane-1-one andα,α-dimethoxy-α-phenylacetophenone; phenacyl chloride andtribromomethylphenylsulfone; 2,4,6-trimethylbenzoyldiphenylphosphineoxide; combinations of the 1,2′-bisimidazoles and4,4′-diethylaminobenzophenone and mercaptobenzothiazole; LUCIRIN TPO;and IRGACURE 651. These compounds may be used singly or in combinationof two or more kinds. Preferably, the initiator is used in an amount of0.1 to 60 parts by weight, more preferably 5 to 50 parts by weight, andparticularly preferably 10 to 40 parts by weight per 100 parts by weightof the alkali-soluble copolymer (A) When the amount is less than 1 wt %,radicals are more liable to be deactivated by oxygen (leading todeteriorated sensitivity). The amount exceeding 60 wt % tends to causepoor compatibility and low storage stability. The radiation-inducedradical polymerization initiators may be used in combination withradiation sensitizers.

Method of Forming Lower and Upper Layers

On a substrate having predetermined wiring patterns, the lower layer isformed by application or lamination, and thereafter the upper layer isformed by application or lamination. Thus, a desired laminated two-layerfilm may be produced. When the material is liquid, the application maybe performed by dipping, spin coating, roll coating or screen processprinting, or by use of an applicator or a curtain coater. When thematerial is a film, lamination or vacuum lamination may be adopted.Drying conditions for the lower and upper layers vary depending on thekinds and proportions of the components making up the composition andthe coating thickness. Generally, the drying is performed attemperatures in the range of 70 to 120° C., and preferably 80 to 100° C,for about 5 to 20 minutes. When the drying time is too short, adhesionmay be bad at the time of development. Any overlong drying causes anexcessive thermal change that leads to lowering of the resolution.

It is also possible that the lower layer material and the upper layermaterial are in advance formed into a two-layer dry film and laminatedon the substrate.

Irradiation Method

The laminated film obtained as described above is then irradiated withultraviolet rays or visible rays of 300 to 500 nm wavelength, through aphotomask having a desired pattern. Exemplary radiation sources includelow-pressure, high-pressure and super-high-pressure mercury lamps, metalhalide lamps and argon gas lasers. As used herein, the radiationsinclude ultraviolet rays, visible rays, far ultraviolet rays, X-rays andelectron beams. The dose of radiation varies depending on the kinds andproportions of the components making up the composition and the filmthickness; for example, it is in the range of 100 to 500 mJ/cm² in thecase of super-high-pressure mercury lamps.

Developing Method

After the irradiation, development is carried out using an alkalineaqueous solution as a developer, so that unnecessary portions aredissolved and removed while radiation-exposed portions remain. Exemplarydevelopers include alkaline aqueous solutions of sodium hydroxide,potassium hydroxide, sodium carbonate, sodium silicate, sodiummetasilicate, aqueous ammonia, ethylamine, n-propylamine, diethylamine,di-n-propylamine, triethylamine, methyldiethylamine,dimethylethanolamine, triethanolamine, tetramethylammonium hydroxide,tetraethylammonium hydroxide, pyrrole, piperidine,1,8-diazabicyclo[5.4.0]-7-undecene and 1,5-diazabicyclo[4.3.0]-5-nonane.The developing solution may be a mixture of the above alkaline aqueoussolution and an appropriate amount of a water-soluble organic solvent,such as methanol or ethanol, or a surfactant. The development timevaries depending on the kinds and proportions of the components makingup the composition and the film thickness; for example, it is usually inthe range of 30 to 360 seconds. The developing method may be any ofdropping, dipping, paddling and spraying. After the development, thepatterned film is washed under running water for 30 to 90 seconds andthereafter air dried using an air gun or dried in an oven.

As a result of the above development using the developing solution, theirradiated area of the upper layer is left and the lower layer isdissolved and removed correspondingly to the removed area(non-irradiated area) of the upper layer.

The remaining resist layers may be subjected to post photoexposure orheating to be further cured.

Formation of Bumps

Subsequently, the low-melting metal such as solder paste is filled inthe aperture pattern as described above, and the metal is reflowed toform bumps. Alternatively, the low-melting metal may be filled in theaperture pattern by direct placement of solder balls or electrolyticdeposition.

Peeling Treatment

After the bumps are formed, the cured layers (resist layers) remainingon the substrate are peeled. The peeling may be performed by, forexample, immersing the substrate in a peeling solution at 50 to 80° C.with agitation for 5 to 30 minutes. Preferred peeling solutions usedherein include dimethyl sulfoxide, and a mixed solution of quaternaryammonium salt, dimethyl sulfoxide and water.

Specifically, the laminated two-layer film maybe peeled and removed fromthe substrate with use of a peeling apparatus having multistageimmersion baths. The treatment may be designed to peel the laminatedtwo-layer film in the first bath containing an appropriate organicsolvent, followed by cycle filtration of the peeled pieces, and to peelthe residual laminated film in the second and later baths filled with apeeling solution containing an organic alkali component.

Alternatively, the treatment may be preferably designed to peel thelaminated two-layer film in the first bath containing dimethylsulfoxide, followed by cycle filtration of the peeled pieces, and topeel the residual laminated film in the second and later baths filledwith a peeling solution containing an organic alkali component anddimethyl sulfoxide.

EXAMPLES

Hereinbelow, the present invention will be described in greater detailby Examples. However, it should be construed that the invention is notlimited thereto. Unless otherwise mentioned, part(s) and % refer topart(s) by weight and % by weight.

Raw materials for the lower layer and upper layer materials are listedbelow.

(Component A: Compound Having a Phenolic Hydroxyl Group)

A-1: m-Cresol and p-cresol were mixed together in a weight ratio of40:60, followed by addition of formalin. The resultant mixture wascondensed by a conventional method under catalysis by oxalic acid togive a cresol novolak. The resin was then subjected to fractionation toremove low-molecular weight fractions. Thus, a novolak resin with aweight-average molecular weight of 12,000 was obtained.

A-2:4,4′-[1-[4[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]diphenol

(Component B: Solvent)

B-1: propylene glycol monomethyl ether

B-2: ethyl 2-hydroxypropionate

B-3: 2-heptanone

(Component C: Acrylic Resin)

C-1:

A flask equipped with a dry ice/methanol reflux condenser and athermometer was purged with nitrogen. The flask was then charged with4.0 g of 2,2′-azobisisobutyronitrile as polymerization initiator, and120 g of ethyl 2-hydroxypropionate as solvent. They were stirred untilthe polymerization initiator was dissolved in the solvent. Subsequently,20.0 g of acrylic acid, 10.0 g of p-isopropenylphenol, 30.0 g of n-butylmethacrylate, 20.0 g of methyl methacrylate and 20.0 g of n-butylacrylate were introduced into the flask. The contents were stirredslowly to give a solution. The solution was then heated to 80° C., andpolymerization was carried out at the temperature for 4 hours. Thesolution temperature was raised to 100° C. and polymerization wasperformed at the temperature for 1 hour. Thereafter, the solution wasallowed to cool to room temperature, and the gas in the flask wasreplaced with air. The solution obtained by the above reaction was addeddropwise to a large quantity of methanol to coagulate the reactionproduct. The coagulated product was washed with water, redissolved intetrahydrofuran of the same weight as the coagulated product, andrecoagulated in a large amount of methanol. The operation ofredissolution through recoagulation was carried out three times intotal. The coagulated product thus obtained was vacuum dried at 40° C.for 48 hours to yield an acrylic resin C-1.

C-2:

A flask equipped with a dry ice/methanol reflux condenser and athermometer was purged with nitrogen. The flask was then charged with4.0 g of 2,2′-azobisisobutyronitrile as polymerization initiator, and100 g of ethyl 2-hydroxypropionate as solvent. They were stirred untilthe polymerization initiator was dissolved in the solvent. Subsequently,10.0 g of methacrylic acid, 15.0 g of p-isopropenylphenol, 25.0 g of8-tricyclo[5.2.1.02.6]decanyl methacrylate, 20 g of isobornyl acrylateand 30.0 g of n-butyl acrylate were introduced into the flask. Thecontents were stirred slowly to give a solution. The solution was thenheated to 80° C., and polymerization was carried out at the temperaturefor 3 hours. After addition of 1 g of 2,2′-azobisisobutyronitrile,polymerization was conducted at 80° C. for 3 hours. The solutiontemperature was raised to 100° C. andpolymerizationwas performed at thetemperature for 1 hour. Thereafter, the solution was allowed to cool toroom temperature, and the gas in the flask was replaced with air. Thesolution obtained by the above reaction was added dropwise to a largequantity of methanol to coagulate the reaction product. The coagulatedproduct was washed with water, redissolved in tetrahydrofuran of thesame weight as the coagulated product, and recoagulated in a largeamount of methanol. The operation of redissolution through recoagulationwas carried out three times in total. The coagulated product thusobtained was vacuum dried at 40° C. for 48 hours to yield an acrylicresin C-2.

C-3:

A flask equipped with a dry ice/methanol reflux condenser and athermometer was purged with nitrogen. The flask was then charged with3.0 g of 2,2′-azobisisobutyronitrile as polymerization initiator, and150 g of ethyl 2-hydroxypropionate as solvent. They were stirred untilthe polymerization initiator was dissolved in the solvent. Subsequently,43 g of 4-isopropenylphenol, 30.8 g of n-butyl acrylate, 2.9 g ofacrylic acid and 23.3 g of 2-hydroxyethyl acrylate were introduced intothe flask. The contents were stirred slowly to give a solution. Thesolution was then heated to 70° C., and polymerization was carried outat the temperature for 3 hours. After addition of 1.5 g of thepolymerization initiator 2,2′-azobisisobutyronitrile, polymerization wasconducted at 70° C. for 3 hours. Thereafter, the solution was allowed tocool to room temperature, and the gas in the flask was replaced withair, followed by addition of 150 mg of p-methoxyphenol. The solutionobtained by the above reaction was added dropwise to a large quantity ofmethanol to coagulate the reaction product. The coagulated product waswashed with water, redissolved in tetrahydrofuran of the same weight asthe coagulated product, and recoagulated in a large amount of methanol.The operation of redissolution through recoagulation was carried outthree times in total. The coagulated product thus obtained was vacuumdried at 40° C. for 48 hours to yield an acrylic resin C-3.

(Component D: Surfactant)

D-1: NBX-15 (available from Neos Co., Ltd.)

D-2: SF-8428 (available from Toray Silicone)

(Component E: Crosslinking Agent)

E-1: ARONIX M-8060 (available from Toagosei Co., Ltd.)

(Component F: Initiator)

F-1: IRGACURE 651 (available from Ciba Specialty Chemicals Inc.)

F-2: KAYACURE DETX-S (available from NIPPON KAYAKU CO., LTD.)

Preparation of Lower Layer Materials A-L, B-L and C-L

As shown in Table 1, 35 parts of A-1, 65 parts of B-1 and 0.1 part ofD-1 were stirred to give a solution. The solution was filtered through amembrane filter having a pore size of 3 μm (capsule cartridge filterCCP-FX-C1B available from ADVANTEC), and a lower layer material A-L wasobtained. Lower layer materials B-L and C-L were prepared in a similarmanner.

Preparation of Lower Layer Materials B-D and C-D

Dry films were prepared from the lower layer materials B-L and C-L, asfollows. The lower layer material B-L was spin coated over an 11cm-square polyethyleneterephthalate (PET) film having a thickness of 50μm so that the post baking film thickness would be 5 μm. The coating wasbaked in a convection oven at 110° C. for 10 minutes to give a lowerlayer material B-D. A lower layer material C-D was produced in a similarmanner. TABLE 1 Lower layer Component Component Component ComponentMaterial material A B C D state A-L A-1 B-1 — D-1 Liquid 35 parts 65parts 0.1 part B-L A-2 B-2 C-1 — Liquid 20 parts 90 parts 10 parts B-DA-2 B-2 C-1 — Dry film 20 parts 90 parts 10 parts C-L A-2 B-2 C-3 D-1Liquid 20 parts 90 parts 20 parts 0.1 part C-D A-2 B-2 C-3 D-1 Dry film20 parts 90 parts 20 parts 0.1 partPreparation of Upper Layer Materials A-L, B-L and C-L

These upper layer materials were prepared from the components as shownin Table 2, in the same manner as the lower layer material A-L.

Preparation of Upper Layer Materials A-D and B-D

Dry films were prepared from the upper layer materials A-L and B-L, asfollows. The upper layer material A-L was spin coated over an 11cm-square polyethyleneterephthalate (PET) film having a thickness of 50μm so that the post baking film thickness would be 40 μm. The coatingwas baked in a convection oven at 110° C. for 10 minutes to give anupper layer material A-D. An upper layer material B-D was produced in asimilar manner. TABLE 2 Upper layer Component Component ComponentComponent Component Material material B C D E F state A-L B-1 C-2 D-1E-1 F-1 Liquid 88 parts 100 parts 0.1 part 51.7 parts 18.6 parts F-2 4.0 parts A-D B-1 C-2 D-1 E-1 F-1 Dry film 88 parts 100 parts 0.1 part51.7 parts 18.6 parts F-2  4.0 parts B-L B-2 C-1 D-2 E-1 F-1 Liquid 122parts  100 parts 0.3 part   45 parts   30 parts B-D B-2 C-1 D-2 E-1 F-1Dry film 122 parts  100 parts 0.3 part   45 parts   30 parts C-L B-3 C-2D-1 E-1 F-1 Liquid 88 parts 100 parts 0.1 part 51.7 parts 18.6 parts F-24.0 partsPreparation of Two-Layer Dry Films A and B

Two-layer dry films were prepared from combinations shown in Table 3, asfollows. The upper layer material B-L was spin coated over an 11cm-square polyethyleneterephthalate (PET) film having a thickness of 50μm so that the post baking film thickness would be 40 μm. The coatingwas baked in a convection oven at 110° C. for 10 minutes. Subsequently,the lower layer material B-L was spin coated over the coated substrateso that the post baking film thickness would be 40 μm. The coating wasbaked in a convection oven at 110° C. for 10 minutes. Thus, a two-layerdry film A was obtained. A two-layer dry film B was prepared in asimilar manner. TABLE 3 Two-layer dry film Upper layer material Lowerlayer material A B-L B-L B C-L C-LPreparation of Peeling Solution

Peeling solution: A peeling solution 1 was prepared by adding 100 g ofan aqueous tetramethylammoniumhydroxide solution (25 wt %) to 4900 g ofdimethyl sulfoxide, followed by stirring.

Preparation of Evaluation Board A

On a 4-inch silicon wafer, a chromium layer was sputtered in a thicknessof 1000 angstroms, and a copper layer was sputtered thereon in athickness of 1000 angstroms. Thus, an evaluation board A was prepared.

Preparation of Evaluation Board B

A surface-roughened, copper-clad glass epoxy laminate (substratethickness: 0.6 mm, size: 10 cm square) was coated with a solder resist(product of JSR, the photosensitive insulating resin compositiondescribed in Example 1 of Japanese Patent Application No. 2000-334348).The solder resist contained (i) a cresol novolak resin containingm-cresol and p-cresol in a molar ratio of 60/40 (weight-averagemolecular weight in terms of polystyrene: 8700), (ii)hexamethoxymethylmelamine, (iii) crosslinked fine particles, (iv)styryl-bis(trichloromethyl)-s-triadine, and (v) ethyl lactate assolvent. The coating was heated in a convection oven at 90° C. for 10minutes to give a uniform film having a thickness of 30 μm.Subsequently, the film was photoexposed through a pattern mask withultraviolet rays from a high-pressure mercury lamp with use of analigner (MA-150, available from Suss Microtech Inc.) in a manner suchthat the dose was in the range of 300 to 500 mJ/cm² at a wavelength of350 nm. Thereafter, PEB (post exposure baking) was performed in aconvection oven at 90° C. for 15 minutes. The film was then developed bybeing showered with a 1-wt % sodium hydroxide aqueous solution having atemperature of 30° C. over a period of 2 to 3 minutes (pressure: 3kgf·cm²). The developed film was photoexposed in a dose of 1000 mJ/cm²at 350 nm wavelength with use of a high-pressure mercury lamp, and wassubsequently heated in a convection oven at 150° C. for 2 hours and at170° C. for 2 hours. Thus, a cured film was produced.

The board thus obtained had a first aperture pattern which was acombination of:

Hole pattern of 95 μm-diameter holes at 150 μm pitch;

Hole pattern of 80 μm-diameter holes at 125 μm pitch; and

Hole pattern of 60 μm-diameter holes at 100 μm pitch.

The apertures of the board were electroless plated with Ni and Au. Anevaluation board B was thus obtained.

Spin Coating Method

The liquid lower layer material or upper layer material was directlydropped on the evaluation board, and was spread by means of a spincoater so as to achieve a post baking film thickness of 40 μm. Thecoating was baked in a convection oven at 110° C. for 10 minutes. Thecoated board was gradually cooled to room temperature, and the coatedsurface was covered with a 50 μm thick PET film with use of a laminator.

Lamination conditions were as follows:

-   -   Roll temperature: 80° C.    -   Roll pressure: 0.4 MPa    -   Transportation speed: 0.5 m/min.        Lamination Method

The dry-film lower layer and upper layer materials, or the two-layer dryfilm was laminated on the board with use of a laminator. The PET filmsubstrate was left unreleased.

Lamination conditions were as follows:

-   -   Roll temperature: 120° C.    -   Roll pressure: 0.4 MPa    -   Transportation speed: 0.5 m/min.

Example 1

<Application>

The lower layer material A-L was spin coated over the evaluation boardA, and the coating was baked on a hot plate at 120° C. for 5 minutes togive a lower layer 5 μm thick. On the lower layer, the upper layermaterial A-L was spin coated, and the coating was baked on a hot plateat 120° C. for 5 minutes to give an upper layer having a thickness of 65μm.

<Photoexposure>

The laminated film was photoexposed through a patterned glass mask withultraviolet rays from a high-pressure mercury lamp with use of analigner (MA-150, available from Suss Microtech Inc.) in a manner suchthat the dose was 1000 mJ/cm² at a wavelength of 420 nm. During thephotoexposure, the glass mask was brought into intimate contact with theboard covered with the PET film.

<Development>

The above-photoexposed board was subjected to paddle development in anaqueous solution containing 2.38% tetramethylammoniumhydroxide(hereinafter, abbreviated as TMAH developing solution). The developerapplication time was generally 90 seconds and adjusted by 15 seconds.After the development, the board was rinsed with ion-exchange water for60 seconds.

The patterned board had a plurality of hole patterns of 75 μm×75 μmapertures.

After the development, the pattern configuration was inspected with anoptical microscope and a scanning electron microscope, and was evaluatedbased on the following criteria. The results are set forth in Table 4.

Pattern configuration:

AA: A hole pattern having 75 μm×75 μm apertures had been developed withno residual film, no floating or no peeling, and the development hadcompleted allowing a margin of development time.

CC: A hole pattern having 75 μm×75 μm holes had residual film, floatingor peeling, and the development did not allow a margin of developmenttime.

<Solder Filing>

The entire surface of the laminated two-layer film was coated with asolder paste with use of a squeegee, and thereby solder-bump formationconcave apertures were completely filled with the solder paste. Thesolder paste used herein contained Sn and Ag in a weight ratio of96.5:3.5 and contained solder particles 5 to 20 μm in diameter. Theviscosity thereof had been adjusted to 200 Pa.s. Thereafter, the solderpaste was removed using a squeegee from the surface other than withinthe solder-bump formation apertures. The paste was completely removedwith cleaning paper, and the surface of the solder paste was flattened.

<Reflowing>

The solder paste printed in the above step was reflowed at 250° C.,followed by flux cleaning.

<Peeling>

After the reflowing, the board was cooled to room temperature.Separately, approximately 1 liter of dimethyl sulfoxide or the peelingsolution 1 was placed in a peeling bath and heated to about 60° C. Theboard was immersed in the bath for 10 minutes under agitation, andthereby the laminated two-layer film was peeled.

The board having been peeling treated in the peeling bath was rinsedwith isopropyl alcohol and washed with water, and was dried using an airgun.

After the peeling treatment, the board surface and the solder bumps wereinspected with an optical microscope and a scanning electron microscope,and were evaluated based on the following criteria. The results are setforth in Table 4.

Evaluation criteria

Peelability with DMSO

AA: Most of the laminated two-layer film was peeled.

CC: The laminated two-layer film was not peeled.

Peelability with the peeling solution 1

AA: No residual film was observed on the board.

CC: Residual film was observed on the board.

Example 2

<Application>

The lower layer material A-L was spin coated over the evaluation boardA, and the coating was baked on a hot plate at 120° C. for 5 minutes togive a lower layer 5 μm thick. On the lower layer, the upper layermaterial A-D (thickness: 65 μm) was laminated.

The other procedures were carried out in the same manner as in Example1.

Example 3

The lower layer material B-L was spin coated over the evaluation boardB, and the coating was baked in a clean oven at 110° C. for 10 minutesto give a lower layer 2 μm thick. On the lower layer, the upper layermaterial B-L was spin coated, and the coating was baked at 110° C. for10 minutes to give an upper layer having a thickness of 40 μm.

<Patterning>

The laminated film was photoexposed through a patterned glass mask withultraviolet rays from a high-pressure mercury lamp with use of analigner (MA-150, available from Suss Microtech Inc.) in a manner suchthat the dose was 400 mJ/cm² at a wavelength of 350 nm. During thephotoexposure, the glass mask was brought into intimate contact with theboard covered with the PET film.

In the photoexposure, the hole pattern (first aperture pattern) of theevaluation board was aligned with a second aperture pattern of theradiation-sensitive resin composition.

The above-photoexposed board was subjected to development by beingshowered with a 1 wt % sodium carbonate aqueous solution having atemperature of 30° C. (pressure: 1 kgf·cm²). The showering time wasgenerally 45 seconds and adjusted by 15 seconds.

The board had the following first and second aperture patterns.

-   -   First aperture Second aperture        -   pattern pattern

-   150 μm pitch 95 μm-diameter holes 100 μm-diameter holes

-   125 μm pitch 80 μm-diameter holes 90 μm-diameter holes

-   100 μm pitch 60 μm-diameter holes 80 μm-diameter holes

After the development, the pattern configuration was inspected with anoptical microscope and a scanning electron microscope, and was evaluatedbased on the following criteria. The results are set forth in Table 4.

Developability:

AA: The second aperture pattern had been developed with no residualfilm, no floating or no peeling, and the development had completedallowing a margin of development time.

CC: The second aperture pattern had residual film, floating or peeling,and the development did not allow a margin of development time.

The other procedures were carried out in the same manner as in Example1.

Example 4

<Application>

The lower layer material B-L was spin coated over the evaluation boardB, and the coating was baked on a hot plate at 120° C. for 5 minutes togive a lower layer 2 μm thick. On the lower layer, the upper layermaterial B-D (thickness: 40 μm) was laminated.

The other procedures were carried out in the same manner as in Example3.

Example 5

The lower layer material B-L was spin coated over the evaluation boardB, and the coating was baked in a clean oven at 110° C. for 10 minutesto give a lower layer 2 μm thick. On the lower layer, the upper layermaterial A-L was spin coated, and the coating was baked in a clean ovenat 110° C. for 10 minutes to give an upper layer having a thickness of40 μm.

The other procedures except the development were carried out in the samemanner as in Example 4.

<Development>

The photoexposed board was subjected to development by being showeredwith a 1% sodium hydroxide aqueous solution (hereinafter, abbreviated asNaOH developing solution) having a temperature of 30° C. (pressure: 1kgf·cm²). The showering time was generally 45 seconds and adjusted by 15seconds. After the development, the board was rinsed with ion-exchangewater for 60 seconds.

Example 6

The lower layer material B-L was spin coated over the evaluation boardB, and the coating was baked on a hot plate at 120° C. for 5 minutes togive a lower layer 2 μm thick. On the lower layer, the upper layermaterial B-D (thickness: 40 μm) was laminated.

The other procedures were carried out in the same manner as in Example5.

Example 7

The lower layer material B-D was laminated on the evaluation board B toprovide a lower layer of 2 μm thickness. On the lower layer, the upperlayer material B-L was spin coated, and the coating was baked in a cleanoven at 110° C. for 10 minutes to give an upper layer having a thicknessof 40 μm.

The other procedures were carried out in the same manner as in Example3.

Example 8

The lower layer material B-D was laminated on the evaluation board B toprovide a lower layer of 2 μm thickness. On the lower layer, the upperlayer material B-D (thickness: 40 μm) was laminated.

The other procedures were carried out in the same manner as in Example3.

Example 9

The two-layer dry film A was laminated on the evaluation board B.

The other procedures were carried out in the same manner as in Example3.

Example 10

The two-layer dry film B was laminated on the evaluation board B.

The other procedures were carried out in the same manner as in Example5.

Comparative Examples 1 to 4

Comparative Examples 1 to 4 were carried out in the same manner as inExamples bearing the corresponding number, except that no lower layerwas provided. TABLE 4 Lower Upper Peelability layer layer DevelopingPattern Peelability (Peeling material material Board solutionconfiguration (DMSO) solution 1) Ex. 1 A-L A-L A TMAH AA AA AA Ex. 2 A-LA-D A TMAH AA AA AA Ex. 3 B-L B-L B Na₂CO₃ AA AA AA Ex. 4 B-L B-D BNa₂CO₃ AA AA AA Ex. 5 B-L A-L B NaOH AA AA AA Ex. 6 B-L A-D B NaOH AA AAAA Ex. 7 B-D B-L B Na₂CO₃ AA AA AA Ex. 8 B-D B-D B Na₂CO₃ AA AA AA Ex. 9Two-layer dry film A B Na₂CO₃ AA AA AA Ex. 10 Two-layer dry film B BNaOH AA AA AA Comp. — A-L A TMAH AA CC CC Ex. 1 Comp. — A-D A TMAH AA CCCC Ex. 2 Comp. — B-L B Na₂CO₃ AA CC CC Ex. 3 Comp. — B-D B Na₂CO₃ AA CCCC Ex. 4

1-13. (canceled)
 14. A process for forming bumps on electrode pads, fora wiring board including a substrate and a plurality of electrode pads,the process comprising: (a) forming a laminated two-layer film on thewiring board and forming a pattern of apertures at positionscorresponding to the electrode pads, the laminated two-layer filmincluding a lower layer comprising an alkali-solubleradiation-nonsensitive resin composition and an upper layer comprising anegative radiation-sensitive resin composition; (b) filling alow-melting metal in the aperture pattern; (c) reflowing the low-meltingmetal by pressing or heating to form bumps; and (d) peeling and removingthe laminated two-layer film from the wiring board.
 15. The process forforming bumps according to claim 14, wherein the radiation-nonsensitiveresin composition contains a compound having a phenolic hydroxyl group.16. The process for forming bumps according to claim 14, wherein thenegative radiation-sensitive resin composition contains an acrylicresin.
 17. The process for forming bumps according to claim 14, whereinthe lower layer of the laminated two-layer film is formed from theradiation-nonsensitive resin composition that is in a form of liquid ordry film.
 18. The process for forming bumps according to claim 14,wherein the upper layer of the laminated two-layer film is formed fromthe negative radiation-sensitive resin composition that is in a form ofliquid or dry film.
 19. The process for forming bumps according to claim14, wherein the laminated two-layer film comprises a two-layer dry filmincluding the lower and upper layers.
 20. The process for forming bumpsaccording to claim 14, wherein the peeling and removing is performedwith use of a peeling apparatus having multistage immersion baths andcomprises peeling the laminated two-layer film in a first bathcontaining an organic solvent, followed by cycle filtration of peeledpieces, and peeling the residual laminated film in a second and laterbaths filled with a peeling solution containing an organic alkalicomponent.
 21. The process for forming bumps according to claim 14,wherein the peeling and removing is performed with use of a peelingapparatus having multistage immersion baths and comprises peeling thelaminated two-layer film in a first bath containing dimethyl sulfoxide,followed by cycle filtration of peeled pieces, and peeling the residuallaminated film in a second and later baths filled with a peelingsolution containing an organic alkali component and dimethyl sulfoxide.22. The process for forming bumps according to claim 14, wherein thewiring board comprises a substrate comprising silicon wafer, and aplurality of electrode pads provided on a surface of the substrate. 23.The process for forming bumps according to claim 14, wherein the wiringboard comprises a substrate comprising silicon wafer, a plurality ofelectrode pads provided on a surface of the substrate, and a passivationfilm formed so as to embed side surfaces and end surfaces of theelectrode pads.
 24. The process for forming bumps according to claim 14,wherein the wiring board comprises a substrate comprising glass epoxyresin or bismaleimide-triadine resin, and a plurality of electrode pads.25. The process for forming bumps according to claim 14, wherein thewiring board comprises a substrate comprising glass epoxy resin orbismaleimide-triadine resin, an insulating resin interlayer and aconductive circuit formed on the substrate, and a plurality of electrodepads provided on the conductive circuit.
 26. The process for formingbumps according to claim 14, wherein the low-melting metal is solder.